The present invention relates to an optical fiber cable manufacturing method and apparatus in which optical fibers are inserted into the spiral grooves on a slotted rod, and then a binding is applied on the outer surface of the slotted rod to thereby form an optical fiber cable.
Generally, in the case where optical fibers or electric wires are used as an optical cable or a communication copper cable, the optical fibers or wires are inserted into the spiral grooves of a slotted rod so as to form an optical fiber cable, thereby increasing the strength of the optical fiber cable.
FIG. 6 (PRIOR ART) shows an optical fiber cable stranding known in the prior art. A slotted rod 11 has a tension wire 12 at its center. Four square-shaped spiral grooves 13 are formed in the outer circumferential surface of rod 11. Spiral grooves 13 extend spirally in a longitudinal direction. An optical fiber 15, or an optical fiber ribbon 16 comprising a plurality of optical fibers 15 bundled together, is inserted into each of the grooves 13. A binding is then applied to the outer circumference of rod 11 to thereby form optical fiber cable stranding 14.
FIG. 7 (PRIOR ART) shows a conventional apparatus for manufacturing an optical fiber cable stranding, such as, for example, shown in FIG. 6 (PRIOR ART). A supply drum 21 having a rotary shaft 26 feeds out the slotted rod 11.
The slotted rod 11 is wound on the supply drum 21. The supply drum 21 is rotatably supported by a rotary shaft 26 so that the slotted rod 11 can be hauled through a guide roller 27 in the direction perpendicular to the rotary shaft 26.
An optical fiber insertion device 22 is arranged to insert the optical fibers 15 or optical fiber ribbons 16 into the respective spiral grooves 13 (see FIG. 6) of the slotted rod 11. A rotary disc 28 is rotatably supported by a rotary shaft 29 provided along the hauling direction of the slotted rod 11. A plurality of supply reels 30 carrying the optical fibers 15 or the optical fiber ribbons 16 wound thereon are mounted on the rotary disc 28. A groove insertion device 31 for inserting the optical fibers 15 or the optical fiber ribbons 16 into the spiral grooves 13 of the slotted rod 11 is provided adjacent to the rotary disc 28. Guide rolls 32 and 33 are attached behind the rotary disc 28 to haul the optical fibers 15 or the optical fiber ribbons 16 into the groove insertion device 31. The rotary disc 28 can be rotated by a driving means (not shown) about the axis in the hauling direction of the slotted rod 11 in synchronism with the spiral grooves 13 of the slotted rod 11.
The string winding device 23 applies a binding onto the outer surface of the slotted rod 11 which has the optical fibers 15 or the optical fiber ribbons 16 inserted therein at the time of passage through the string winding device 23. Further, the hauling device 24 hauls the thus formed optical fiber cable 14 so as to give desired tension thereon. In the hauling device 24, belts 36 are driven through four rollers 34. Further, the winding drum 25 winds up the optical fiber cable 14. The hauling device may also be such a double-wheel hauling device 35 as shown in FIG. 8.
Thus, as shown in FIG. 7 (PRIOR ART), when the hauling device 24 is operated so as to haul the optical fiber cable 14, the supply drum 21 is rotated about the rotary shaft 26, and while the rotary disc 28 is being rotated by the driving means, the supply reels 30 are rotated. Then, the slotted rod 11, the optical fibers 15, and the optical fiber ribbons 16 are hauled, so that the optical fibers 15 or the optical fiber ribbons 16 are inserted by the groove insertion device 31 into the spiral groove 13 in the slotted rod 11. A binding is applied by the string winding device 23 onto the slotted rod 11 to thereby form the optical fiber cable 14. Then, the optical fiber cable 14 is wound on the winding device 25.
In the conventional optical fiber cable manufacturing method described above, the optical fibers 15 or the optical fiber ribbons 16 which are inserted into the spiral grooves 13 of the slotted rod 11 have low tension and are subject to movement within the grooves 13. The position of the optical fibers 15 or the optical fiber ribbons 16 relative to the slotted rod 11, therefore, is not fixed, even after passing through the hauling device 24, until the optical fiber cable 14 is wound on the winding drum 25. Accordingly, it is difficult to make the relative lengths between the slotted rod 11 and the optical fibers 15 or the optical fiber ribbons 16 accurate and even over the entire length of the optical fiber cable 14, or in a required range thereof. Therefore, using the conventional method and apparatus of manufacturing an optical fiber cable, stable transmission characteristics of the optical fiber cable 14 cannot be maintained.
Further, as shown in FIG. 8, even if the hauling device 24 is of a double-wheel winding type 35, the tension in the optical fiber cable 14 is generally reduced either before or after passage through the hauling device 24. Thus, it cannot be specified at what position of the double wheel type hauling device 35 the tension of the optical fiber cable 14 is reduced. Even the slack, frictional force, or the like of the optical fiber cable 14 cannot be specified when utilizing a double wheel type hauling device 35.
When utilizing the conventional method and apparatus for manufacturing an optical fiber cable, the optical fiber cable 14 is in a constant state of flux during the manufacture process. Therefore, the position where the optical fibers 15 or the optical fiber ribbons 16 are fixed relative to the slotted rod 11 cannot be specified due to the friction factor or the fine change of the tension of the optical fibers 15, and is always changing in the manufacture of the optical fiber cable. That is, at the time when the relative length between the slotted rod 11 and the optical fibers 15 or the optical fiber ribbons 16 is fixed, the tension of the optical fiber cable 14, that is, the slotted rod 11 cannot be specified.
Accordingly, as described above, in the conventional optical fiber cable 14, the relative length between the slotted rod 11 and the optical fibers 15 or the optical fiber ribbons 16 cannot be made even over the entire length of the optical fiber cable or in a required range thereof, so that stable transmission characteristics of the optical fiber cable 14 cannot be maintained.